US9825532B2 - Current control for DC-DC converters - Google Patents

Current control for DC-DC converters Download PDF

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US9825532B2
US9825532B2 US14/380,304 US201314380304A US9825532B2 US 9825532 B2 US9825532 B2 US 9825532B2 US 201314380304 A US201314380304 A US 201314380304A US 9825532 B2 US9825532 B2 US 9825532B2
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primary
switching
alternating voltages
phase angle
voltage bridges
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US20150146455A1 (en
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Stefan Engel
Ir. Rik W. A. A. De Doncker
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Flexible Elektrische Netze Fen GmbH
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Flexible Elektrische Netze Fen GmbH
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters

Definitions

  • the invention relates to DC-DC converters having a so-called dual active bridge (DAB) topology as well as to a method for operating these DC-DC converters.
  • DAB dual active bridge
  • a DC-DC converter also known as a power converter, refers to an electric circuit that converts a direct current fed in at the input into a direct current having a higher, lower or inverted voltage level.
  • DC-DC converters can be found, for example, in the switched-mode power supply units of PC power supply packs, notebooks, mobile phones, small motors and HiFi devices. Their advantages in comparison to linear power supply units are their better efficiency and lower heat generation. In a linear voltage regulator or in a series resistor, in contrast, the superfluous voltage simply “burns out”.
  • DC-DC converters are also available as completely encapsulated converter modules that are sometimes intended for direct insertion into printed circuit boards.
  • the output voltage (secondary voltage) can be lower than, equal to or greater than the input voltage (primary voltage), depending on the model.
  • the best-known modules are the ones that transform an extra-low voltage into a galvanically isolated extra-low voltage.
  • the encapsulated DC-DC converters are available, for example, for insulation voltages ranging from 1.5 kV to over 3 kV, and they serve to supply power to small consumers in direct-voltage networks such as, for example, 24 V in industrial installations or 48 V in telecommunications or in the realm of electronic modules such as, for instance, 5 V for digital circuits or ⁇ 15 V for the operation of operational amplifiers.
  • DC-DC converters are classified according to various criteria and divided into different topologies (type of structure of a branched network on current paths). In contrast to unidirectional converters, when it comes to bidirectional DC-DC converters, it is immaterial which terminal is defined as the input and which terminal is defined as the output. A bidirectional energy flow allows power to flow from the defined input (primary side) towards the output (secondary side) and vice versa.
  • DC-DC converters that are based on the functional principle of a dual active bridge (DAB) topology
  • DAB dual active bridge
  • the DC input voltage is converted in an input converter into an AC voltage which is then fed to a transformer.
  • the output of the transformer is connected to an output converter that once again converts the AC voltage into a DC output voltage for a load.
  • DAB DC-DC converter topologies as disclosed, for example, in U.S. Pat. No. 5,027,264, constitute high-efficiency converter topologies that allow a bidirectional energy flow, galvanic separation via the transformer and operation at high voltages. This type of converter is particularly well-suited for use in medium-voltage DC networks.
  • the transferred power is set by varying the phase angle between the voltage on the primary side and the voltage on the secondary side. If the transferred power is to be changed abruptly, undesired oscillations as well as an unbalanced distribution of the currents in the phases occur.
  • the oscillation dies down as a function of the time constant L/R, wherein L stands for the sum of the leakage inductance of the primary winding and the leakage inductance of the secondary winding of the transformer—relative to the primary side—and R stands for the sum of the resistance of the primary winding and the resistance of the secondary winding—relative to the primary side.
  • phase angle of conventional DAB DC-DC converters is normally only changed slowly in order to avoid oscillations to the greatest extent possible.
  • the slow change of the phase angle leads to reduced dynamics of the current regulation, so that only a slow regulation of the current would be possible. Therefore, when it comes to DAB DC-DC converters that are supposed to have high dynamics, this method of oscillation reduction cannot be employed, thereby resulting in undesired oscillations and an unbalanced distribution of the currents in the phases.
  • a method for operating an at least three-phase DC-DC converter having a primary side comprising at least three actively switched primary voltage bridges with several active switches for converting a DC input voltage into primary alternating voltages for each of the primary voltage bridges, and having a secondary side comprising at least three actively switched secondary voltage bridges with several active switches for converting the secondary alternating voltages into a shared DC output voltage for each of the secondary voltage bridges, whereby each of the primary voltage bridges is coupled to one of the secondary voltage bridges via a multi-phase transformer, or via particular a transformer to particular one phase, whereby the primary and secondary alternating voltages are shifted by a phase angle ⁇ with a period T, said method comprising the steps of setting the phase angle ⁇ from a first phase angle ⁇ 1 to a second phase angle ⁇ 2 as the switching operation for transferring power from the primary side to the secondary side, whereby the primary and secondary voltage bridges are switched during the switching operation in such a way that the phase angles ⁇ of the individual phases are set independently of
  • a DAB DC-DC converter that allows a fast change of the phase angle while, at the same time, minimizing or preventing oscillations in the direct current in the case of power changes. If oscillations in the direct current were not minimized or prevented, then the phase angle could only be changed very slowly. Thanks to the time-independent setting of the phase angle ⁇ for the individual phases during the switching operation, the present invention allows a fast change of the phase angle, thus permitting a highly dynamic setting of the direct current (fast regulation of the current) and thus a fast power transfer.
  • the method according to the invention precisely allows a highly dynamic change of the transferred power in contrast to the state of the art, where DAB DC-DC converters are employed in stationary operation.
  • the phase angle ⁇ of the various phases is set during the switching operation, independently of falling and rising edges of the primary and secondary alternating voltages. Therefore, the DC-DC converters according to the invention are especially well-suited as power converters, especially as DC-DC converters, to be used for medium to high power levels and so-called pulsed-power applications that entail high requirements of the dynamics.
  • the primary side refers to the part of the DC-DC converter that is facing the source of energy.
  • the secondary side refers to the other side of the transformer that is connected to the electric load.
  • the primary and secondary sides are insulated from each other by the transformer. If the DAB DC-DC converter is configured so as to be bidirectional, then the primary side in one bidirectional DC-DC converter can, in fact, be the secondary side in another bidirectional DC-DC converter.
  • the DC-DC converter according to the present invention can be configured as a three-phase or multiphase DAB DC-DC converter, for instance, also as a five-phase DAB DC-DC converter.
  • the DC input voltage is present at the voltage bridges with the active switches and it is converted into an alternating voltage in the voltage bridges by switching the active switches (switching operation). Since, as a rule, the switches are completely switched on, alternating voltages that have approximately the shape of a square-wave (square-wave voltage) are formed at the output bridges. As a result, the voltage over the transformer windings becomes stepped. If applicable, owing to the use of so-called snubbers, the edges of the square-wave voltage are not infinitely steep, that is to say, the form deviates from that of a square-wave voltage (stepped form at the transformer windings). Snubbers are employed to ensure a dynamic voltage balancing in switching operations (snubber network).
  • snubber network refers to an electric circuit having snubber elements that, in the case of an abrupt interruption of the current flow, are meant to neutralize, for example, interfering high frequencies or voltage peaks that usually occur when inductive loads are switched. Snubber elements limit the rate of voltage rise or the rate of current rise on semiconductors.
  • Suitable switches for the voltage bridges are active semiconductors (power semiconductors) such as, for example, gate turn-off thyristors, transistors, MOSFETs, IGBTs (insulated gate bipolar transistors) or ICGTs (integrated gate-commuted thyristor) with intelligent gate drivers.
  • active semiconductors power semiconductors
  • IGBTs insulated gate bipolar transistors
  • ICGTs integrated gate-commuted thyristor
  • transformer refers to the magnetic circuit—usually a ferrite or iron core—with the appertaining windings of the primary and secondary voltage bridges around the magnetic core. If each of the phases comprises a separate transformer, only the conductors of a primary phase and the appertaining other secondary phase are wound around the transformer that is associated with this phase. The magnetic cores of the transformers of the individual phases are then physically separated from each other.
  • multiphase transformer in contrast, refers to a transformer that has a shared magnetic core for all phases, whereby the windings of the primary and secondary voltage bridges of the individual phases are arranged in different areas of the magnetic core.
  • the multiphase transformer is a three-phase transformer.
  • the function of a DAB DC-DC voltage converter in both cases, is to bring about a systematic voltage drop via the AC voltages on the transformer via the leakage inductance of the transformer and thus to control the power flow.
  • Actively switched voltage bridges make it possible to independently control the shift angle (phase angle) between the primary and secondary alternating voltages present on the transformer and thus to systematically control the power flow.
  • the phase angle ⁇ here refers to the shift of the primary and secondary alternating voltages with respect to each other, each with the period T.
  • the first phase angle ⁇ 1 refers to the shift of the primary and secondary alternating voltages with respect to each other before the beginning of a switching operation.
  • the second phase angle ⁇ 2 refers to the shift of the primary and secondary alternating voltages with respect to each other after the end of the switching operation.
  • the phase angles ⁇ can also assume one or more values between ⁇ 1 and ⁇ 2 , whereby ⁇ 1 can be greater or smaller than ⁇ 2 .
  • the phase angle ⁇ can assume positive and negative values.
  • a positive value ⁇ between a first and a second alternating voltage means that the second alternating voltage lags behind the first alternating voltage in the characteristic curve of the alternating voltages.
  • a negative value ⁇ between a first and a second alternating voltage means that the second alternating voltage leads (or precedes) the first alternating voltage in the characteristic curve of the alternating voltages.
  • the phase angles ⁇ of the individual phases are set differently in order to balance the currents in the phases.
  • the method is not restricted to the use of the same phase angles for all phases. As a result, for instance, unbalances of the transformers can be balanced in such a way that there is nevertheless a balanced current distribution in the phases.
  • the DC-DC converter is a three-phase DC-DC converter with three actively switched primary voltage bridges, each having two or more active switches, and three actively switched secondary voltage bridges, each having two or more active switches, whereby, the switching operation effects the setting of the phase angle ⁇ 2 of all three phases at the same edges (that is to say, either only for the rising edges of the alternating voltages of the phases or else only for the falling edges of the alternating voltages of the phases) of the primary and secondary alternating voltages at the primary and secondary voltage bridges.
  • Such a three-phase DC-DC converter with DAB topology has the advantage, for instance, that it significantly increases the available power density due to the improved utilization of the available apparent power of the transformer.
  • the number of switches can amount to two switches per voltage bridge. In other embodiments, for example, four switches per voltage bridge can also be employed, as is the case for an NPC topology.
  • the DC-DC converter according to the present invention is a three-phase DAB NPC DC-DC converter.
  • NPC stands for neutral-point clamped.
  • the voltage levels can be set via clamping diodes so as to be balanced, as a result of which the medium voltage matches the zero voltage level, without this calling for balancing networks and/or drivers.
  • the clamping diodes it is possible to use IGBTs (bipolar transistors with an insulated gate electrode) (ANPC inverters), or else capacitors in so-called FLCs for purposes of distributing the voltage.
  • said method comprises the following additional steps:
  • This method additionally avoids an unbalance of the phase currents.
  • the target current here is already reached after T/3, without excitation of oscillations. If the plus/minus sign of the phase angle also changes when the phase angle changes, an elevated phase current nevertheless occurs briefly after the change of the phase angle.
  • the method can be applied to phase shifts of 120° between the voltages of the first, second and third primary voltage bridges, or of the first, second and third secondary voltage bridges, although the method is not restricted to phase shifts of 120°.
  • the method is not restricted to the above-mentioned sequence of switching operations of the individual bridges.
  • the method can also be used for a cyclical interchange of the switching operations, or for a reversal of the switching operations.
  • primary/secondary or “secondary/primary” refer to the appertaining switching operations for the sides cited either before or after the slash “/”.
  • first items before the slash
  • second items after the slash
  • This method also allows a fast change of the power flow as well as a balanced current distribution in the three phases. If the primary and secondary alternating voltages are shifted by a positive phase angle, then the secondary alternating voltage switches to the primary alternating voltage so as to be lagging. In contrast, if the primary and secondary alternating voltages are shifted by a negative phase angle, then the secondary alternating voltage switches to the primary alternating voltage so as to be leading (or preceding). Both possibilities are encompassed by the above-mentioned method.
  • the phase angles ⁇ are different for rising and falling edges.
  • the number of switches can be two switches per voltage bridge. In other embodiments, for example, four switches can also be employed per voltage bridge as is the case with an NPC topology.
  • the DC-DC converter according to the present invention is a three-phase DAB NPC DC-DC converter.
  • NPC stands for neutral-point clamped.
  • the three voltage levels can be set via clamping diodes so as to be balanced, as a result of which the medium voltage matches the zero voltage level, without this calling for balancing networks and/or drivers.
  • IGBTs bipolar transistors with an insulated gate electrode
  • ANPC inverters insulated gate electrode
  • capacitors in so-called FLCs for purposes of distributing the voltage.
  • the method comprises the following additional steps:
  • This alternative method likewise additionally avoids an unbalance of the phase currents.
  • the target current here is already reached after T/2.
  • This method is characterized in that no oscillations are excited and in that no elevated phase current occurs, not even briefly after the change of the phase angle.
  • this method reaches the target current later (T/2 instead of T/3), but in this case, without a slightly elevated phase current for a brief period of time, even if the plus/minus sign of the phase angle changes.
  • the method can be employed for phase shifts of 120° between the voltages of the first, second and third primary voltage bridges, or of the first, second and third secondary voltage bridges, although the method is likewise not restricted to phase shifts of 120°.
  • the method is not restricted to the above-mentioned sequence of switching operations of the individual bridges.
  • the method can also be used for a cyclical interchange of the switching operations, or for a reversal of the switching operations.
  • the terms “primary/secondary” or “secondary/primary” refer to the appertaining switching operations for the sides cited either before or after the slash “/”.
  • the first items (before the slash) correspond to the switching operations for a current flow in the one direction
  • the second items (after the slash) correspond to the switching operations for the reversed current flow.
  • This method also allows a fast change of the power flow as well as a balanced current distribution in the three phases.
  • the secondary alternating voltage switches to the primary alternating voltage so as to be lagging. If, in contrast, the primary and secondary alternating voltages are shifted by a negative phase angle, then the secondary alternating voltage switches to the primary alternating voltage so as to be leading (or preceding). Both possibilities are encompassed by the above-mentioned method.
  • the switching operation for setting the second phase angle ⁇ 2 comprises one or more periods T of the primary and secondary alternating voltages, and the phase angle ⁇ between the primary and secondary alternating voltages is set stepwise to the second phase angle ⁇ 2 on the edge.
  • the stepwise setting of the phase angle ⁇ 2 is done linearly in steps of the same size. This makes it easier to suppress possible slightly elevated phase currents. This method is advantageous if the current is supposed to be changed linearly within a period of time that is greater than T/2.
  • phase angles ⁇ of the rising and falling edges are adapted during the switching operation on the basis of the above-mentioned phase angles in order to compensate for transformer and switch influences. This makes it possible to compensate for influences that cannot already be avoided just by the topology.
  • the DC-DC converter is operated in such a way that the phase shifts of the primary alternating voltages of the primary voltage bridges among each other as well as the phase shifts of the secondary alternating voltages of the secondary voltage bridges among each other deviate from 120°. In this manner, the above-mentioned advantages to be retained while, at the same time, unbalances of the transformer can be balanced.
  • the invention also relates to a system consisting of an at least three-phase DC-DC converter having a primary side comprising at least three actively switched primary voltage bridges with several active switches for converting a DC input voltage into primary alternating voltages for each of the primary voltage bridges, and having a secondary side comprising at least three actively switched secondary voltage bridges with several active switches for converting the secondary alternating voltages into a shared DC output voltage for each of the secondary voltage bridges, whereby each of the primary voltage bridges is coupled to one of the secondary voltage bridges via a multi-phase transformer, or via particular a transformer to particular one phase, in order to transform the primary alternating voltage into the secondary alternating voltage, whereby the primary and secondary alternating voltages are shifted by a phase angle ⁇ with a period T, said system consisting of at least one control unit that is configured to carry out the control of the active switches of the primary and secondary voltage bridges of the at least three-phase DC-DC converter by means of the method according to the present invention.
  • control unit could be configured as a control means that makes use of one or more DSPs (digital signal processor), FPGAs (so-called field programmable gate arrays), CLPDs (so-called complex programmable logic devices), a microcontroller or else making use of a combination of the above-mentioned components.
  • DSPs digital signal processor
  • FPGAs field programmable gate arrays
  • CLPDs complex programmable logic devices
  • the DC-DC converter is a three-phase DC-DC converter with three actively switched primary voltage bridges, each having two or more active switches, and three actively switched secondary voltage bridges, each having two or more switches.
  • the DC-DC converter can have a low-pass filter on the primary side and/or on the primary [sic] side.
  • one or more capacitors can be arranged on the primary side and/or on the secondary side in order to filter the current.
  • the method according to the invention can also be applied to the DAB DC-DC converter topology with capacitors that are connected in series or in parallel to the transformer windings (or in a different arrangement), for instance, for resonance converters or resonant DAB converters.
  • FIG. 1 shows an embodiment of a topology of a DC-DC converter (DAB DC-DC converter) that is suitable for carrying out the method according to the invention, and (b) shows the same topology while illustrating the particular transformer for each phase;
  • DAB DC-DC converter DC-DC converter
  • FIG. 2 shows simulated curves of (a) the phase angle, (b) the phase current, and (c) the direct current for a DC-DC converter shown in FIG. 1 , with a switching method according to the state of the art, with oscillations;
  • FIG. 3 shows a first embodiment of the method according to the invention, for a three-phase DAB DC-DC converter
  • FIG. 4 shows simulated curves of (a) the phase angle, (b) the phase current, and (c) the direct current for a DC-DC converter shown in FIG. 1 , with a switching method according to the invention by means of the first embodiment of the method shown in FIG. 3 ;
  • FIG. 5 shows a second embodiment of the method according to the invention, for a three-phase DAB DC-DC converter
  • FIG. 6 shows the simulated curves of (a) the phase angle, (b) the phase current, and (c) the direct current for a DC-DC converter shown in FIG. 1 , with a switching method according to the invention in the second embodiment of the method shown in FIG. 5 ;
  • FIG. 7 a system consisting of a DC-DC converter and a control unit according to the present invention.
  • FIG. 1 shows a three-phase DC-DC converter G 3 with a primary side 1 comprising three actively switched primary voltage bridges 11 , 12 , 13 , each having two active switches S 1 for converting a DC input voltage ES into primary alternating voltages 111 , 112 , 113 for each of the primary voltage bridges 11 , 12 , 13 , and with a secondary side 2 comprising three actively switched secondary voltage bridges 21 , 22 , 23 , each having two active switches S 2 for converting the secondary alternating voltages 211 , 212 , 213 into a shared DC output voltage AS for each of the secondary voltage bridges 21 , 22 , 23 .
  • switches S 1 , S 2 for the voltage bridges are active semiconductor switches (power semiconductors) such, for instance, gate turn-off thyristors, transistors, MOSFETs, IGBTs (insulated gate bipolar transistors) or ICGTs (integrated gate-commuted thyristors) with intelligent gate drivers.
  • active semiconductor switches power semiconductors
  • the number of voltage bridges and/or the number of active switches S 1 , S 2 per voltage bridge can vary; for example, in an NPC topology, this can be four switches per voltage bridge.
  • Each of the primary voltage bridges 11 , 12 , 13 is coupled to one of the secondary voltage bridges 21 , 22 , 23 via a multiphase transformer 3 , for instance, a three-phase transformer 3 , in this case the three-phase DC-DC converter G 3 , or else via a separate transformer 3 to each of the phases, whereby the alternating voltages 111 , 112 , 113 , 211 , 212 , 213 applied on the primary and secondary sides are shifted by a phase angle ⁇ with a period T.
  • FIG. 1 illustrates multiphase transformer 3 while
  • FIG. 1 illustrates three-phase transformer 3 as consisting of the aforementioned separate transformers for each phase.
  • the phase angle is switched from a first phase angle ⁇ 1 to a second phase angle ⁇ 2 during the switching operation.
  • capacitors 10 , 20 are arranged on the primary and secondary sides in order to filter the voltage.
  • the topology of the DC-DC converter shown here in the form of DAB DC-DC converters can be used for the switching method according to the state of the art as well as for the switching method according to the invention. However, in other embodiments, the DC-DC converter can also have more than three phases.
  • the control unit that serves to control the switches is not shown here.
  • FIG. 2 shows the simulated curves of (a) the phase angle in degrees, (b) the phase current in amperes, and (c) the direct current in amperes, for a three-phase DC-DC converter shown in FIG. 1 , with a switching method according to the state of the art, which causes oscillations in the direct current if the phase angle is changed quickly. A fast change of the phase angle allows power to be transferred rapidly.
  • the same values and assumptions were employed for the simulations for the phase angle, the phase current and the direct current of the method according to the invention shown in FIGS. 3 and 5 , and depicted in FIGS.
  • the switching method according to the state of the art does not change the angle ⁇ of the three phases independently of each other, but rather, in one shared step for all phases, as shown in FIG. 2( a ) , so that strong oscillations of the direct current occur after each change of the phase angle ⁇ .
  • the DC input current is shown by way of an example for the direct current, although, qualitatively speaking, the same behavior occurs for the DC output current as well.
  • the time constant is proportional to L/R, wherein L stands for the sum of the leakage inductance of the primary winding and the leakage inductance of the secondary winding of the transformer—relative to the primary side—and R stands for the sum of the resistance of the primary winding and the resistance of the secondary winding—relative to the primary side.
  • L stands for the sum of the leakage inductance of the primary winding and the leakage inductance of the secondary winding of the transformer—relative to the primary side
  • R stands for the sum of the resistance of the primary winding and the resistance of the secondary winding—relative to the primary side.
  • the oscillations that occur after a power change have a long time constant.
  • the oscillations of the direct current are suppressed according to the state of the art in that the phase angle ⁇ is only changed slowly, which is simulated here as a stepwise change in many small steps within the time interval of 0.03 s to 0.04 s, see FIG. 2( a ) .
  • the oscillations in the direct current that occur are markedly smaller than in the case of an abrupt change in a single step.
  • FIG. 3 shows a first embodiment of the method according to the invention for a three-phase DAB DC-DC converter by means of which the oscillations, as shown before in FIG. 2( c ) , can be prevented.
  • the primary alternating voltages 111 , 112 , 113 solid lines
  • the secondary alternating voltages 211 , 212 , 213 broken lines
  • the DC input voltage is present at the voltage bridges 11 , 12 , 13 with the active switches and it is converted into an alternating voltage 111 , 112 , 113 in the voltage bridges 11 , 12 , 13 in that the active switches S 1 are switched (switching operation), and then this DC input voltage is transformed into a corresponding alternating voltage 211 , 212 , 213 by means of the transformer 3 . Since, as a rule, the switches S 1 are completely switched on, alternating voltages 211 , 212 , 213 that have approximately the shape of a square-wave (square-wave voltage) are formed at the output bridges 21 , 22 , 23 . As a result, the voltage over the transformer windings becomes stepped.
  • the edges of the square-wave voltage 111 , 112 , 113 , 211 , 212 , 213 are not infinitely steep, that is to say, the form deviates from that of a square-wave voltage (stepped form at the transformer windings).
  • the primary and secondary alternating voltages 111 , 112 , 113 , 211 , 212 , 213 are switched according to the invention by means of the switches S 1 , S 2 in such a way that, during the switching operation, the switching (setting) of the phase angle ⁇ 2 for all three phases takes place for the same edges of the primary and secondary alternating voltages 111 , 112 , 113 , 211 , 212 , 213 at the primary and secondary voltage bridges, here each time at the falling edges of the alternating voltages V 1 , V 2 and V 3 , from ⁇ 1 to ⁇ 2 , whereby the primary switching operation for the primary alternating voltages 111 , 112 , 113 takes place at the point in time t 0 for the second phase, at the point in time t 0 +T/3 for the third phase and at the point in time t 0 +2/3 T for the first phase.
  • the switching operations for the secondary alternating voltages 211 , 212 , 213 take place so as to be lagging (shifted) by ⁇ 1 or ⁇ 2 relative to the switching operations of the primary alternating voltages, depending on the edge orientation relative to the edge of the first switching operation.
  • the term “lagging” refers to a positive phase angle ⁇ >0.
  • leading phase angles ⁇ corresponds to a negative phase angle ⁇ 0.
  • the switching operations of the secondary alternating voltages 211 , 213 of the first and third phases take place so as to be lagging (shifted) by ⁇ 2 with respect to the switching of the corresponding primary alternating voltages 111 , 113 at the next falling edges of the secondary alternating voltages 211 , 213 of the first and third phases.
  • the switching operation takes place so as to still be lagging by ⁇ 1 with respect to the switching of the corresponding primary alternating voltages 111 , 113 .
  • the first switching operation 1 s 2 of the primary (secondary) alternating voltage 112 ( 212 ) of the second primary (secondary) voltage bridge 12 ( 22 ) takes place at the point in time t 0
  • the first switching operation 1 n 2 of the secondary (primary) alternating voltage 212 ( 112 ) of the second secondary (primary) voltage bridges 22 ( 12 ) takes place so as to be lagging by a phase angle ⁇ 2 >0.
  • the first switching operation 1 s 1 of the primary (secondary) alternating voltage 111 ( 211 ) of the first primary (secondary) voltage bridge 11 ( 21 ) takes place at the point in time t 0 +T/6, and the first switching operation 1 n 1 of the secondary (primary) alternating voltage 211 ( 111 ) of the first secondary (primary) voltage bridge 21 ( 11 ) takes place so as to be lagging by the phase angle ⁇ 1 >0, independently of the preceding switching operations.
  • the first switching operation 1 s 3 of the primary (secondary) alternating voltage 113 ( 213 ) of the third primary (secondary) voltage bridge 13 ( 23 ) takes place at the point in time t 0 +T/3, and the first switching operation 1 n 3 of the secondary (primary) alternating voltage 213 ( 113 ) of the third secondary (primary) voltage bridge 23 ( 13 ) takes place so as to be lagging by a phase angle ⁇ 2 >0, independently of the preceding switching operation.
  • the second switching operation 2 s 2 of the primary (secondary) alternating voltage 112 ( 212 ) of the second primary (secondary) voltage bridge 12 ( 22 ) takes place at the point in time t 0 +T/2, and the second switching operation 2 n 2 of the secondary (primary) alternating voltage 212 ( 112 ) of the second secondary (secondary) voltage bridge 22 ( 12 ) takes place so as to be lagging by the phase angle ⁇ 2 >0, independently of the preceding switching operations.
  • the second switching operation 2 s 1 of the primary (secondary) alternating voltage 111 ( 211 ) of the first primary (secondary) voltage bridge 11 ( 21 ) takes place at the point in time t 0 +2/3*T, and the second switching operation 2 n 1 of the secondary (primary) alternating voltage 211 ( 111 ) of the first secondary (primary) voltage bridge 21 ( 11 ) takes place so as to be lagging by the phase angle ⁇ 2 >0, independently of the preceding switching operations.
  • the second switching operation 2 s 3 of the primary (secondary) alternating voltage 113 ( 213 ) of the third primary (secondary) voltage bridge 13 ( 23 ) takes place at the point in time t 0 +5/6*T, and the second switching operation 2 n 3 of the secondary (primary) alternating voltage 213 ( 113 ) of the third secondary (primary) voltage bridge 23 ( 13 ) takes place so as to be lagging by the phase angle ⁇ 2 >0, independently of the preceding switching operations.
  • the above-mentioned switching method can also be carried out with negative phase angles.
  • the first or second switching operation of the secondary (primary) alternating voltages would take place so as to be leading (preceding) with respect to the switching of the primary (secondary) alternating voltage.
  • the terms “primary” and “secondary” that are not between parentheses as well as the corresponding reference numerals refer to switching operations for a current flow in the one direction of the DC-DC converter.
  • the reference numerals and terms “(primary)” and “(secondary)” that are between parentheses refer to the corresponding switching operations for the reverse current flow in the other direction of the DC-DC converter. This method also allows a fast reversal of the power flow as well as a balanced current distribution in the three phases.
  • FIG. 4 shows the simulated curves of (a) the phase angle in degrees, (b) the phase current in amperes, and (c) the direct current in amperes, for a three-phase DC-DC converter shown in FIG. 1 , which is operated with the switching method according to the invention as shown in FIG. 3 in order to quickly change the phase angle and in order to avoid oscillations in the direct current.
  • the phase current already reaches its target value after T/3, and the direct current in FIG. 4( c ) does not show any of the oscillations which can be seen with a switching method according to the state of the art.
  • the direct current shown in FIG. 4( c ) is here, for example, the DC input current, although qualitatively speaking, the same behavior occurs as with the DC output current.
  • one or more capacitors can be arranged on the primary side and/or on the secondary side for smoothing purposes.
  • FIG. 5 shows a switching method according to the present invention, as an alternative to the switching method shown in FIG. 3 .
  • the switching operations for the secondary alternating voltages 211 , 212 , 213 take place with a change of the phase angle in two stages so as to each be shifted by ( ⁇ 1 + ⁇ 2 )/2 alternately on falling and rising edges of the second, first and third phases—in the first switching operation so as to be lagging (shifted) by ( ⁇ 1 + ⁇ 2 )/2 and in the second switching operation so as to be lagging (shifted) by ⁇ 2 .
  • the primary alternating voltages 111 , 112 , 113 (solid lines) and the secondary alternating voltages 211 , 212 , 213 (broken lines) in accordance with the simulations are shown as square-wave voltages in FIGS. 2, 4 and 6 .
  • the DC input voltage is present at the voltage bridges 11 , 12 , 13 with the active switches and it is converted into an alternating voltage 111 , 112 , 113 in the voltage bridges 11 , 12 , 13 by switching the active switches S 1 (switching operation), and connected via the transformer to a corresponding alternating voltage 211 , 212 , 213 .
  • the first switching operation 1 s 2 of the primary (secondary) alternating voltage 112 ( 212 ) of the second primary (secondary) voltage bridge 12 ( 22 ) takes place at the point in time t 0
  • the above-mentioned switching method can also be carried out with negative phase angles.
  • the first or second switching operation of the secondary (primary) alternating voltages would take place so as to be leading (preceding) with respect to the switching of the primary (secondary) alternating voltage.
  • the terms “primary” and “secondary” that are not between parentheses as well as the corresponding reference numerals refer to switching operations for a current flow in the one direction of the DC-DC converter.
  • the terms “(primary)” and “(secondary)” that are between parentheses refer to the corresponding switching operations for the reverse current flow in the other direction of the DC-DC converter. This method also allows a fast reversal of the power flow as well as a balanced current distribution in the three phases.
  • FIG. 6 shows the simulated curves of (a) the phase angle in degrees, (b) the phase current in amperes, and (c) the direct current in amperes, for a three-phase DC-DC converter shown in FIG. 1 , which is operated with the switching method according to the invention as shown in FIG. 5 in order to quickly change the phase angle and in order to avoid oscillations in the direct current.
  • the phase current already reaches its target value after T/2
  • the direct current in FIG. 6( c ) likewise does not show any of the oscillations which can be seen with a switching method according to the state of the art shown in FIG. 2( c ) .
  • one or more capacitors can be arranged on the primary side and/or on the secondary side for smoothing purposes.
  • the methods can effectuate a switching operation which, for purposes of setting the second phase angle ⁇ 2 , comprises one or more periods T of the primary and secondary alternating voltages 111 , 112 , 113 , 211 , 212 , 213 , and in which the phase angle ⁇ between the primary and secondary alternating voltages 111 , 112 , 113 , 211 , 212 , 213 is set stepwise to the second phase angle ⁇ 2 on the edge.
  • the stepwise setting of the phase angle ⁇ 2 can be done linearly in steps of the same size.
  • phase angle ⁇ of the rising and falling edges can be adapted during the switching operation on the basis of the above-mentioned phase angles in order to compensate for transformer and switch influences.
  • the DC-DC converter G, G 3 can be operated in such a way that the phase shifts of the primary alternating voltages 111 , 112 , 113 of the primary voltage bridges 11 , 12 , 13 among each other as well as the phase shifts of the secondary alternating voltages 211 , 212 , 213 of the secondary voltage bridges 21 , 22 , 23 among each other deviate from 120°.
  • FIG. 7 shows a system S according to the invention consisting of the DC-DC converter G and the control unit 4 , whereby the control unit 4 is configured to carry out the control of the active switches S 1 , S 2 of the primary and secondary voltage bridges 11 , 12 , 13 , 21 , 22 , 23 of the at least three-phase DC-DC converter G by means of the method according to the invention, as shown by way of an example in FIGS. 3 and 5 for a three-phase DC-DC converter.
  • the DC-DC converter G is a three-phase DC-DC converter with three actively switched primary voltage bridges 11 , 12 , 13 , each having two or more active switches S 1 , and three actively switched secondary voltage bridges 21 , 22 , 23 , each having two or more active switches S 2 .
  • the control unit 4 can be configured as a control means 4 that makes use of one or more DSPs (digital signal processors), FPGAs (so-called field programmable gate arrays), CLPDs (so-called complex programmable logic devices), a microcontroller, or else employing a combination of the above-mentioned components.
  • DSPs digital signal processors
  • FPGAs field programmable gate arrays
  • CLPDs complex programmable logic devices
  • microcontroller or else employing a combination of the above-mentioned components.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
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DE102012204035A DE102012204035A1 (de) 2012-03-14 2012-03-14 Stromregelung für Gleichspannungswandler
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CN104170231B (zh) 2017-03-08
KR102207433B1 (ko) 2021-01-26
CN104170231A (zh) 2014-11-26
EP2826139A2 (de) 2015-01-21
KR20140135237A (ko) 2014-11-25
WO2013135811A3 (de) 2014-04-24
HK1200605A1 (zh) 2015-08-07
IN2014MN01826A (ko) 2015-07-03

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